At present, the oil industry faces several technical incapacities to respond to the increasingly higher worldwide demands. One of the biggest shortcomings is the fact that practically all of the world oil resources are of a heavy or ultra heavy nature, wherein asphaltene and/or asphaltene-like macromolecules are present in large amounts. Other important oil sources are oil-containing tar sands, shales or clays which present a similar problem.
The high content of asphaltene, together with the presence of sulphur and metals, makes oil recovery difficult both by affecting the rheological properties of the material from the oil well or by increasing environmental pollution hazards. Without a doubt, the oil industry must solve these problems taking into account the nature of almost all the huge oil reserves so far unexploited, mainly in Venezuela.
Oil recovery from the above mentioned type of deposits is difficult and costly since the steps of recovering, transporting, and refining are inefficient, making their exploitation quite laborious and unattractive. Another fact adversely affecting this matter is the potential environmental pollution risks produced by the metals and the sulphur contained in such oil deposits. No method has been developed so far which allows the obtention of a saleable oil-product, from deposits having unfavorable rheological properties and chemical composition throughout the entire industrial process.
Heavy oil and ultra-heavy oil recovery is performed at present mainly by injection of pressurized and overheated water vapor and also by mixing the oil with lighter organic solvents. Inorganic acids, e.g., hydrochloric and sulfuric acids, have also been used to acidize wells to improve the flow of the oil from the earth matrix. All of these methods do facilitate the oil management, but only up to its cooling and/or solvent separation after which the rheological difficulties reappear. Even though in Venezuela the method of the oil emulsion has been successfully applied to the transportation of crude oil, its use is not fully recommended since the value of that oil as combustible is markedly reduced.
Recently, in U.S. Pat. No. 4,675,120, Martucci described a method of using a low pH mixture of acids wherein the availability of hydronium ions in the mixture itself remains highly controllable, while the mixture itself remains non-corrosive to metals and innocuous to skin and other organic materials. These mixtures include several acids using two strong acids and two weak acids, preferably hydrochloric acid, oxalic acid, phosphoric acid, and citric acid. This patent describes the use of such acid mixtures for acidizing wells surrounded by clay or silicate formation and/or surrounded by calcareous formation. One Example in this patent describes the use of oleic acid and a mixture of hydrochloric, phosphoric, oxalic and citric acids for the recovery of oil from oil-containing sands.
The method of the present invention relates to the recovery of oil, under appropriate forms, from heavy and ultra-heavy oil deposits and from oil-containing sands. The inventive method is based on the cracking properties, at room temperature and normal pressure over the asphaltene macromolecules present in the crude oil, of a cracking-active mixture containing an inorganic acid and a liquid fatty acid, preferably hydrochloric acid and oleic acid. The method can also easily be applied to oil recovery from oil-containing tar sands. The chemical reactions occurring between the acid mixture and the heavy oil material are not yet fully understood, but the fact is that an improvement of the rheological properties of crude oil is attained by this convenient process which also facilitates the cleaning of sulphur and metals from the crude oil. It has also been found that the inorganic acid-fatty acid treatment of crude oils reduces the water content of the crude oil, probably due to the consumption of water molecules as proton sources during the depolymerization processes occurring at the asphaltene level wherein carbon ion might be involved.
It has been found that a binary mixture of an inorganic acid component and a liquid fatty acid component, e.g., hydrochloric and oleic acids, both in the form of a solution and in the form of a suspension, works much better than the poly-acid mixtures proposed in U.S. Patent No. 4,675,120. This is probably related to the consumption of water produced during the depolymerization process conducted with the binary mixture, which does not occur when using poly-acid mixtures. Along with water consumption, molecular oxygen is released producing a clear bubbling as the gas evolves off the oil sample, while hydrogen is likely being incorporated to some double linkages naturally occurring in the unsaturated hydrocarbon chains of asphaltene compounds.